This invention relates to the mounting of transmit/receive (TR) modules in arrays with cooling optimized for minimum temperature difference between modules.
A great deal of commerce is currently aided by the use of electromagnetic communication, and electromagnetics are widely used for sensing, as for example in radar systems. Such radar systems may be used for monitoring the flight path of an aircraft from the aircraft itself for weather and object monitoring, monitoring the airspace around an airport for traffic control purposes, distance and acceleration monitoring between automobiles, and for military purposes. Reflector-type antennas have been, and still are, widely used for obtaining the high gain desired for communication with distant locations, and to obtain a narrow radar antenna beam to allow objects to be located with more precision than if a broad antenna beam were used. Reflector-type antennas are subject to some disadvantages, especially when the antenna beam must be scanned rapidly. Since the direction of the antenna beam as generated by a reflector antenna depends upon the physical position of the reflector, the reflector itself must be physically moved in order to scan the antenna beam. For simple area surveillance, this is not a problem, because the reflector antenna can simply be rotated at a constant speed to recurrently scan the surrounding area.
In those cases requiring antenna beam agility, reflector antennas are less satisfactory, because the inertia of the antenna results in the need to apply large forces to obtain the necessary accelerations and decelerations. In addition to being costly to operate, the physical stresses on the structure tend to lead to early failure or increased need for maintenance.
As a consequence of these and other disadvantages of reflector-type antennas, attention has been given to the use of array antennas, in which multiple antenna elements or ant elements are arrayed to define a larger radiating aperture, and fed from a common source. In order to achieve beam agility, each antenna element (or groups of antenna elements) are associated with controllable phase shifters. In order to improve the range of the communications or of the radar using the phase-shift-controllable array antenna, each antenna element may be associated with a power amplifier, a low-noise receiving amplifier, or both. The combination of the controllable phase shifter for each antenna element, the low-noise receiving amplifier, and the power amplifier, are often combined into a xe2x80x9ctransmit-receivexe2x80x9d (TR) module, together with various switch and control elements, so that modular electronics can be used with the modular antenna elements of the array. U.S. Pat. No. 3,339,086, issued Aug. 16, 1994 in the name of DeLuca et al. describes a phased array antenna in which each elemental antenna element is associated with a transmit/receive (TR) module, but does not describe the physical nature of the structure.
With the increasing range and performance requirements of modern equipments, the power-handling capabilities of the power amplifiers of each of the TR modules of an array antenna have tended to increase. The reliability of electronic equipment tends to be degraded by operation at high temperatures. The increase in power required to be handled by the power amplifiers of TR modules, in turn, leads to the problem of carrying away the additional heat associated with the higher power, so as to keep the electronics at a low, and therefore reliable, temperature. U.S. Pat. No. 5,459,474, issued Oct. 17, 1995 in the name of Mattioli et al. describes an array antenna in which the electronics associated with a column of arrays are in the form of TR modules mounted on a coolant-fluid-carrying cold plate of a slide-in carrier. In the Mattioli et al arrangement, each slide-in carrier has a width no greater than the spacing between adjacent antenna elements. Heat is carried away from each slide-in carrier by coolant flow through a set of hoses, which allow the carriers to be slid toward and away from the antenna array for maintenance. The mounting of a large number of TR modules directly to the cold plate may be disadvantageous, as the entire cold plate must be taken out of service in order to work on or replace a single TR module. The changing out of a defective TR module is complicated by the mechanical fasteners and thermal joining material, or the epoxy bond, often used to provide good physical and thermal mounting of the TR module to the cold plate.
It is desirable to mount small numbers of the TR modules on Line-Replaceable Units (LRUs), which in turn are mounted to the cold plate. The number of TR modules which are mounted on each LRU depends upon a number of factors, among which one major factor is the availability of small-volume, efficient, reasonable-cost power supplies. That is to say, LRUs with but a single TR module may require a power supply which has excess capability for that one TR module, and an array of such LRUs would therefore contain more volume of power supplies than needed. Since volume is a consideration in an array situation, one TR module per LRU might be considered to be undesirable. Similarly, a very large number of TR modules on a single LRU tends to reduce the advantage of a line-replaceable unit, as removal of the LRU takes a large number of TR modules off-line, to the detriment of array operation. With such an arrangement, maintenance on a single TR module can be effected by simply replacing the LRU requiring repair or maintenance with a replacement unit, whereupon the maintenance can be performed off-line while the electronic system or radar continues in operation. Even with the LRU missing, the array can still remain in operation although with degraded capability.
FIG. 1 is a simplified perspective or isometric view of an arrangement in which the TR modules are mounted on a Line Replaceable Unit (LRU) 10 in groups of four. As illustrated in FIG. 1, the set 12 of TR modules 12, 12b, 12c, and 12d is mounted in a vertical line array parallel with an array direction represented by arrow 8, near the antenna-array end 14ar on a vertically-oriented thermally conductive baseplate 14. Each module of set 12 includes an RF power output port, some of which are designated 12ao, 12bo, and 12co, and also includes an RF signal input port, some of which are designated as 12ai, 12bi, and 12ci. Lying between each TR module 12a, 12b, 12c, and 12d and the antenna-array end 14ar of the baseplate 14 is a circulator 16a, 16b, 16c, and 16d, respectively, of a set 16 of circulators. Each circulator includes an antenna element coupling port coupled to a connector (not illustrated) mounted adjacent the antenna-array end 14ar of the baseplate 14, for providing a connection to the associated antenna element, and also includes two further coupling ports, which are coupled by paths (not illustrated) to the transmit or output and receive or input ports of the modules of set 12, for coupling to amplifiers of each TR module. Thus, when the LRU 10 of FIG. 1 is slid into place in its mounting behind the array antenna, in a manner generally similar to that of the abovementioned Mattioli et al. patent, each circulator of set 16 of circulators provides a path from the power amplifier (not illustrated) of the associated TR module to the antenna element, and from the antenna element to the receive amplifier (not illustrated) of the TR module.
In addition to the set 12 of TR modules, the baseplate 14, and the set 16 of circulators, LRU 10 of FIG. 1 illustrates a set 20 of control board assemblies 20a, 20b, 20c, and 20d mounted on a printed-circuit board 19 supported by baseplate 14, for controlling the various parameters of the corresponding TR modules, such as the phase shift, gain or attenuation, and the like, under control from a remote antenna control computer (not illustrated) coupled to connectors 22a and 22b, located near or at the power-and-control end 14pc of the baseplate 14. Other electronic components, designated together as 24, may be mounted on printed-circuit board 19.
While only four TR modules are illustrated as being mounted on the illustrated side of baseplate 14 of FIG. 1, another complete set of components, including circulators, TR modules, control board assemblies, and additional components, may be mounted on the reverse side (not visible in FIG. 1) side of the baseplate 14.
As mentioned, the power amplifier portions of the TR modules of set 12 of TR modules of FIG. 1 (and the power amplifiers of additional TR modules mounted on the reverse side of the baseplate 14, if such exist) are the major (although not the only) sources of heat on LRU 10. However, similar problems exist in LRUs which provide power-supply service under similar conditions. Thus, heat must be coupled away from the TR modules in order to maintain them at a temperature sufficiently low to provide the desired reliability. In an LRU such as that of FIG. 1, the heat from each TR module of set 12 flows from a substantially planar surface, such as surface 13a of the TR module (possibly through a printed-circuit board 21) to thermally conductive baseplate 14. In prior-art arrangements, a clear region 14ue is provided adjacent the upper edge of baseplate 14, and a corresponding clear region 14le is provided adjacent the lower edge of the baseplate 14. Upper and lower clear regions 14ue and 14le, respectively, are provided so that baseplate 14 can be clamped to a cold plate to provide both mechanical support and a thermal sink.
FIG. 2 illustrates three TR LRUs mounted in a portion of a cold-plate structure located adjacent to, and behind (on the antenna feed side of) an antenna array structure. In FIG. 2, the structure 200 includes a portion of a ground plane 240 of the array antenna structure, which defines a set 230 including a plurality of feed apertures, some of which are illustrated as 230a, 230b, 230c, and 230d. The feed apertures of set 230 are provided for coupling electromagnetic energy from the circulators of the TR modules of a line replaceable unit (LRU) to the antenna elements (not illustrated) lying behind ground plane 240. Each aperture of set 230 either includes an electromagnetic transmission line, or is dimensioned to accommodate such a transmission line. A vertical array of such apertures is associated with each vertical array of circulators of each LRU. The structure 200 of FIG. 2 also includes an LRU support and cooling structure, the illustrated portion of which is designated generally as 202. The support and cooling structure 202 which includes a portion of a support and cooling structure 202 includes an upper cold plate 210u and a lower cold plate 2101. As used herein, the term xe2x80x9ccold platexe2x80x9d means a plate or structure through which coolant fluid is circulated or flows to carry away heat coupled to the cold plate.
Lower cold plate 2101 of FIG. 2 defines a plurality of thermally conductive elongated bosses or raised protuberances 212a, 212b, and 212c, and additional bosses 214a, 214b, and 214c. Similarly, upper cold plate 210u defines a plurality of elongated bosses or raised protrusions 216a, 216b, and 216c, and additional bosses 218a, 218b, and 218c. Each mutually adjacent pair of such bosses defines a gap or space therebetween. For example, mutually adjacent or mutually facing bosses 218a and 218b define a gap or space designated 221a, and a corresponding gap 221b is defined between bosses 218b and 218c. These gaps have predetermined dimensions, and more particularly are dimensioned to accommodate the thickness of two baseplates 14 of TR modules such as modules 10 of FIGS. 1 or 2, and the additional thickness or width of an edge clamp, two of which are illustrated in FIG. 2 as 220a and 220b. 
As illustrated in FIG. 2, the gap between bosses 212a and 212b contains the lower edges of the baseplates 14 of two adjacent LRUs 10, and one edge clamp designated 220a. The baseplates 14 of the two LRUs 10 lie immediately adjacent to, and ideally in intimate thermal contact with, the bosses 212a and 212b. The edge clamp 220a is a mechanically expandable device corresponding in principle to a mechanical jack, centrally located between its associated bosses. In the absence of an LRU, a gap having about the thickness of the baseplate of an LRU exists between the edge clamp and an adjacent boss, as indicated in FIG. 2 by the gap or slot 222 lying between boss 212c and edge clamp 220b. Each edge clamp can be loosened or contracted to provide more or less space between itself and the adjacent walls of the bosses; in the context of edge clamp 220b, the transverse dimension of slot or gap 222 can be slightly changed by expansion or contraction of the width of edge clamp 220b. The edge clamp is contracted to provide for clearance in order to allow ready insertion of the LRUs into the structure, and then forced toward its expanded state in order to force the installed LRUs against the walls of the adjacent bosses, to thereby improve the thermal contact at the interface between the bosses and the LRU baseplates. A low thermal resistance is desirable at the interface, to thereby tend to reduce the temperature of the baseplates 14 toward the temperature of the cold plate in the vicinity of the LRU. The pressure exerted by the edge clamp in order to provide low thermal resistance may be quite high, so the edge clamp requires substantial mechanical advantage. In one embodiment, the mechanical advantage is provided by a longitudinal screw extending through the length of the edge clamp, together with overlapping inclined planes or ramps which are forced together by rotation of the screw. As known, thermally conductive grease or other material may be added to the interface in order to aid in reducing the thermal resistance at the interface.
It will be understood that edge clamps are also used between mutually adjacent LRUs along the top edges of their baseplates, as well as along the bottom edges, as illustrated in FIG. 2. It will also be understood that the three LRUs illustrated in FIG. 2 are merely a few of those which may be found in an active antenna array system, and the support structure 202 will ordinarily provide for access for additional LRUs. Thus, the bosses or protuberances 218a, 218b, and 218c provide for mounting and heat transfer for the lower edges of the baseplates of additional LRUs situated above the illustrated LRUs, and similarly the additional bosses 214a, 214b, and 214c lying under cold plate 2101 provide for mounting and heat transfer to yet other LRUs lying below the illustrated LRUs. Also, the structure 202 of FIG. 2 will ordinarily extend to the right and to the left, as seen in FIG. 2, to provide for further arrayed LRUs.
FIG. 3 is a simplified cross-sectional or end view of a portion of the structure of FIG. 2, illustrating two mutually adjacent LRUS, designated 210a and 210b, both of which are held in place by edge clamps 220a and 320a. In FIG. 3, there are TR modules mounted on both sides of the baseplates 14 of the LRUs 210a and 210b. More specifically, the left side of LRU 210asupports TR modules 312a, 312b, 312c, and 312d, and the right side of LRU 210a supports other TR modules, which are not separately designated. Similarly, the left side of LRU 210b supports four TR modules which are not separately designated, and also supports, on its right side, and additional four TR modules, which are designated 312e, 312f, 312g, and 312h. One of the advantages of a structure such as that described in conjunction with FIGS. 1, 2, and 3 is that the LRUs can be removed for maintenance without excessively disrupting normal operations, and an additional advantage is that such removal of the LRUs can be accomplished without making and breaking coolant flow paths.
Improved array antenna structures are desired.
An active array antenna according to an aspect of the invention includes a plurality of RF modules having at least transmit capability. Each of the modules, when energized, generates heat, and transfers the heat to a generally planar mounting and heat transfer surface of the module. The active array antenna also includes a plurality of thermally conducting, generally planar mounting and heat transfer plates, each of which mounting and heat transfer plates defines at least one generally straight edge. Each of the mounting and heat transfer plates includes mounting positions for at least three of the modules. These mounting positions are arrayed in a straight line parallel to the straight edge, whereby, if heat is extracted from the mounting and heat transfer plates in a direction collinear with the straight-line array, those of the modules nearest the heat extraction regions will have a lower temperature than others of the modules more remote from the heat extraction regions. The active array antenna includes a mounting structure for mounting the plurality of generally planar mounting and heat transfer plates in a side-by-side array, with the straight edges of the mounting and heat transfer plates lying in a plane. A generally planar cold plate abuts and is in thermal contact with the straight edges of the mounting and heat transfer plates, for extracting heat from the mounting and heat transfer plates in a direction orthogonal to the array direction, which thereby tends to maintain all of the modules at the same temperature.
In a particular embodiment of the invention, each of the modules includes at least an RF output port, and the mounting and heat transfer plates include RF coupling means, for coupling RF from (a) the positions of the RF output ports of the modules associated with the heat transfer plate when the modules are mounted at the mounting locations to (b) locations adjacent the straight edge of the mounting and heat transfer plate.